Mothers may pass on life-long fears to infants via smell

Mothers teach newborn babies what to be scared of by literally letting them smell their fear, US research suggests.

In a study of rats, scientists showed how a mother’s alarm scent primed her days-old offspring to develop a peppermint phobia.

They believe the same “smell of fear” mechanism may be at work in humans.

“These maternally-transmitted memories are long-lived, whereas other types of infant learning, if not repeated, rapidly perish”

Jacek Debiec

For generations experts have been puzzled by the degree to which a mother’s traumatic experiences can affect her children.

Some children of Holocaust victims, for instance, react as if they had witnessed the same horrors as their mothers.

Their fear, manifested in the form of nightmares, avoidance behaviour and even flashbacks, appears too deeply ingrained to have been learned simply by hearing stories.

Study leader Dr Jacek Debiec, from the University of Michigan, said: “Our research demonstrates that infants can learn from maternal expression of fear, very early in life.

“Before they can even make their own experiences, they basically acquire their mothers’ experiences. Most importantly, these maternally-transmitted memories are long-lived, whereas other types of infant learning, if not repeated, rapidly perish.”

Jacek Debiec

Dr Debiec, who was born in Poland, found evidence of human babies “inheriting” fear from their parents while working with the grown children of Jews who survived the Nazi death camps.

He hopes the research will lead to ways of blocking the transmission of irrational or harmful fear responses from mothers to their children.

The scientists studied mother rats who were taught to associate the smell of peppermint with a mild but unpleasant electric foot shock.

After giving birth, the rats were again exposed to the minty smell in the presence of their newborn pups.

A frightened mother’s odour transmitted the same fear to her offspring, whose stress hormone levels rose, the researchers found.

The newly acquired fear was also long lived, lasting through early adolescence.

A further experiment showed that smell alone was able to imprint fear into a baby rat, without its mother having to be present. Just the piped-in scent of a mother reacting to peppermint was enough to make a rat pup frightened of the same thing.

By using a drug to block activity of the amygdala, the scientists were able to prevent baby rats learning to fear peppermint from their mothers’ smell.

While it is not yet known if the same smell-based fear signalling occurs in people, human mothers’ scent has been shown to have a calming effect on babies.

The scientists wrote: “Despite clinical evidence that specific fear is transmitted across generations, we have little understanding of mechanisms.

“Here we model social transmission of mother-to-infant fear in rodents. We show that maternal fear responses to a conditioned fear odour are sufficient to induce robust fear learning throughout infancy, with robust retention.”

Readers' comments
(3)

The emphasis here is on maternal fear. We are presuming biological mother. What about other close contacts, such as biological fathers, adoptive parents, siblings, etc. There are other factors that were not discussed within this article, and whilst the research may be in the early stages, not making reference to other people (fathers, grandparents, adoptive parents) is contentious. It places all the emphasis on the biological mother, which may reinforce stereotypes; but by not opening the discussion out, you may be ignoring the impact that other people have upon a developing child, when such people are a daily part of a child's life - as opposed to acquaintance-level contacts.

Wagonwheel, psychiatrists have proved that the biological mother has rt-side emotional centre hormonal stimulation which binds her to her unborn and consequently born child that are not there is adopted or foster parents, so reactions to danger, or fear will be more evident in the natural mother than any other. I am sure any loving carer of a very young baby will give off "fear smells" also

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